Optical technology utilizes optical signals in order to carry information. Optical technology also utilizes filters for a variety of applications. Filters transmit light in a pass band. The pass band of the filter is a range of wavelengths centered around a central wavelength. For example, one application for filters is in multiplexing and demultiplexing optical signals. It is possible to transmit a plurality of signals on a single fiber. As the use of optical technology increases, the number of signals transmitted on a single fiber also increases. Currently, signals having four, eight, sixteen or more channels are transmitted on a single fiber. Typically, each channel is centered around a different wavelength.
In order to transmit a large number of signals on a given cable, channels for a plurality of wavelengths are multiplexed together for transmission. After the multiplexed, multi-channel signal reaches the destination, the channels are demultiplexed to access the information carried by a single channel. Conventional wavelength division multiplexers ("WDMs") are used to combine individual signals as well as to separate a composite signal into individual channels.
In order to function, some conventional WDMs utilize filtering. To separate a composite signal into its component channels, conventional filtering WDMs use a plurality of filters cascaded in series to isolate each channel. Each filter passes light centered around a single wavelength. A filter is typically provided for each of the component wavelengths. The output of each filter is the signal centered around a single wavelength. As each component wavelength is separated from the composite signal, the remaining portion of the composite signal is passed on to the next filter in the series. Thus, the signal is separated into its components. Note that other applications may also use filters. In general, filters are useful in applications where it is desired to remove a portion of the signal outside of the filter's pass band. Thus, in addition to WDMs, filters may be used in noise removal or other applications.
Typically, a signal is input to a conventional filtering system via an optical fiber. The fiber is typically held by a capillary. The signal is then provided to a graduated index of refraction (GRIN) lens for collimating. The signal is then transmitted to a filter. The filter transmits light centered around a particular wavelength. In a conventional WDM, a separate filtering system is used for each channel.
Although conventional systems for filtering signals are capable of transmitting light in the pass band, a conventional filter is used with a fixed angle of incidence. Thus, the central wavelength for the pass band is also fixed. As a result, the filter itself will be subject to tighter specifications in order to ensure that the appropriate portion of the signal is transmitted. The tighter specifications make the filter more expensive. In addition, one filter is typically used for each channel. As a result, the cost of providing filters for a composite signal is high. In addition, the filters will occupy a relatively large space.
Accordingly, what is needed is a system and method for providing a filter which is low cost, efficient, and compact. The present invention addresses such a need.